This invention relates to a copper-based alloy excelling in corrosion resistance, a method for the production thereof, and products made of the copper-based alloy, and more particularly to a copper-based alloy, namely a material which requires dezincification corrosion resistance in the presence of a corroding aqueous solution and which is utilized as a machining material, used in a field requiring a hot processing property such as hot forging property, further utilized in a state having stress such as of caulking applied thereto, and moreover utilized extensively in a field requiring stress-corrosion cracking resistance as well as dezincification resistance, a method for the production thereof, and products made of the copper-based alloy.
As copper-based alloy materials, a forging brass bar (JIS C3771), a free-cutting brass bar (JIS C3604), a naval brass bar (JIS C4641), a high-strength brass bar (JIS C6782), and the like are generally known.
Since these copper-based alloys have various defects and do not prove satisfactory, various improved copper-based alloys have been proposed heretofore.
The present applicant has already proposed a copper-based alloy excelling in dezincification corrosion resistance and hot processing property as published in JP-A-07-207,387.
Though the alloy of this publication exhibits fine characteristic properties and find actual utility in a wide range of fields, it has evolved the below-mentioned problematic point with the elapse of time of actual service. The desirability of developing an improvement directed at overcoming the problems, therefore, has been finding growing recognition.
To be more specific about this point, in a test for dezincification corrosion to be performed in the atmosphere of a corrosive liquid, this alloy possibly succumbs to local corrosion. Further, this copper-based alloy, when used as a cutting material or used in a state exposed to stress such as caulking, possibly sustains a stress-corrosion crack.
This invention has been perfected by a diligent study initiated in the light of the problematic point mentioned above. It has for an object thereof the provision of a copper-based alloy exhibiting a fine dezincification corrosion resistance in the atmosphere of a corrosive liquid and excelling in hot processing property and stress-corrosion cracking resistance, a method for the production thereof, and products made of the copper-based alloy.
One aspect of this invention concerns a copper-based alloy having a composition of 58.0 to 63.0% of Cu, 0.5 to 4.5% of Pb, 0.05 to 0.25% of P, 0.5 to 3.0% of Sn, 0.05 to 0.30% of Ni, and the balance of Zn and inevitable impurities (weight %) and having the ratio of P and Sn so adjusted as to satisfy the expression, P (%)xc3x9710=(2.8 to 3.98) (%)xe2x88x92Sn (%). The copper-based alloy has its texture fragmented uniformly to exhibit excellent corrosion resistance and excellent hot processing property. Furthermore, when having undergone a proper drawing work and heat treatment it is improved in tensile strength, hardness, elongation, etc. Moreover, it excels in stress-corrosion cracking resistance when its internal stress has been thoroughly removed.
The copper-based alloy can further contain 0.02 to 0.15% by weight of Ti.
The copper-based alloy is produced by extruding a billet at a predetermined temperature and heat-treating the product of extrusion at a temperature of not more than the predetermined temperature, thereby adjusting its metal composition so that the average crystal grain diameter is not more than substantially 20 xcexcm.
In the extrusion step, the billet extruding temperature is preferably lowered to not more than 680xc2x0 C. to uniformly fragment the crystal grains of the texture of the extruded bar material.
In the production process, the extruded billet is subjected to a proper drawing work and heat treatment or to forging and then heat treatment in a temperature region of 475 to 600xc2x0 C. for a period in the range of 1 to 5 hours.
Another aspect of this invention concerns a copper-based alloy produced by extruding a relevant cast billet, heat-treating the product of extrusion in a temperature region of 475 to 600xc2x0 C. for a period in the range of 1 to 5 hours, and subjecting the heat-treated product to a proper drawing work.
The drawing work is effected by a plastic processing at a 10 to 30% ratio of area reduction for the purpose of exalting material strength.
After the plastic processing, the plasticized product is further heat-treated at a temperature in the range of 250 to 400xc2x0 C. for a period in the range of 1 to 5 hours for the purpose of performing the adjustment of material and the removal of residual stress.
By this method of manufacture, it is made possible to obtain a copper-based alloy which excels in stress-corrosion cracking resistance because the method thoroughly performs the adjustment of material (tensile strength not less than 400 N/mm2, elongation not less than 25%, and hardness not less than Hv 100) and the treatment for removal of residual stress.
The copper-based alloy was used as a raw material to produce water-contacting parts such as valves, joints, pipes, water faucets, supplies for water or hot-water feeding, etc., or electrical mechanical products such as gas appliance parts, washing machine parts, air conditioner parts, etc. The results were good.
In the case of extruding the alloy of this invention mentioned above, by lowering the heating temperature of the billet to a level of not more than 680xc2x0 C. prior to the extrusion, thereby uniformly fragmenting the crystal grains of the texture, of the bar material to a diameter of not more than 20 xcexcm, the copper-based alloy to be produced is enabled to acquire an excellent hot processing property.
The copper-based alloy mentioned above owns the hot forging property which is inherent in a Pb-containing brass, exhibits an excellent dezincification corrosion resistance, and fits the work of hot processing. This alloy further abounds in economy because the use of P for the sake of improving corrosion resistance results in further lowering the cost of raw material.
A drawing work and a heat treatment additionally performed suitably allow the copper-based alloy to exhibit stress-corrosion cracking resistance effectively.
According to this invention, therefore, it has become possible to provide a copper-based alloy which manifests an excellent effect in dezincification corrosion resistance, stress-corrosion cracking resistance, and hot processing property and abounds in economy as well.
The copper-based alloy of this invention excels in respect of strength besides excelling in corrosion resistance, hot processing property, and stress-corrosion cracking resistance as described above. When this alloy is used, for example, for valves, taps, and parts thereof which need prescribed magnitudes of pressure resistance as pressure vessels, therefore, it allows these vessels to decrease their wall thicknesses as compared with the vessels of the conventional alloy. Further, it enjoys highly satisfactory workability as compared with the conventional alloy because it excels in susceptibility to the cutting work and therefore permits a reduction in the time required for the work of cutting performed thereon and further because it manifests a high hot processing property and therefore permits a cut in the time required for the work of processing performed thereon.